Hello, this question is from a signal processing exam paper.

Compute the convolution sum (0.8)^n u[n] * u[n] and show that it is equal to
5[1-(0.8)^n+1] u[n]

Here u[n] denotes the discrete-time unit step function.

I'm stuck on this, could anyone shown me how this is the answer? and what the step by step process is for convolution.